Magnetic Drive System with Levitated Flow-Through Permanent Magnet Motors and Magnetic Bearings to Increase the Reliability and Retrievability of Electrical Submersible Pumps for Offshore Production

Abstract

A new technology, Magnetic Drive System (MDS), to increase reliability and retrievability of electrical submersible pumps (ESPs) is described. With the improved reliability and retrievability, the production uptime of oil wells with artificial lift and the total cost of ownership of ESPs are improved significantly. An industry survey and literature review were conducted to identify the aspects of the ESP and the failure-prone ESP subsystems to improve upon. Based on the findings, the MDS technology is developed to improve ESP reliability by isolating the failure modes and to improve ESP retrievability by enabling fast deployments and retrievals from wells. Mean Time Between Failure (MTBF) models based on field observed failure mechanisms are applied to identify the impacts of isolating various failure modes on ESP reliability. The total cost of ownership (TCO) is calculated to illustrate the advantages of the MDS system to increase production gains and reduce costs. Analysis on ESP reliability shows that the electrical system is the primary ESP failure mode, covering more than 50% of the failures. Models based on field data from the literature review shows that MTBF can be more than tripled if these failures are eliminated. The MDS topology places all the electrical components, including motor stators, cables and penetrators, of an ESP in the isolated annulus space between the permanent completion and tubing, leaving only the mechanical components, including the permanent magnet motor rotors and pump stages, inside the production tubing. In this case, the electrical components are well protected from the hostile produced fluids, so that the failures modes of the electrical system are eliminated. Since the retrievable string has no electrical components, such as thousands of feet of power cable, the deployments and retrievals of the retrievable string can be easily done by slickline. The larger motor stator and higher power density enabled by enhanced heat dissipation of the MDS topology dramatically increase the motor horsepower and shorten the motor length, thus increasing the production gains of the ESP. Reliability and retrievability are further improved due to the elimination of motor protectors and replaced by the "built-in" magnetic coupling between the MDS motor stator and rotor. With the improved reliability, retrievability, and motor performance simultaneously, MDS reduces the total cost of ownership by more than 70% in some cases compared with the conventional tubing-hung ESP, enables live well deployment and retrieval, reduces production downtime and intervention complexity, and protects reservoir productivity.